Japanese Patent Application Laid-Open No. 2003-309520 (Patent Document 1) discloses an invention of a terrestrial optical fiber transmission line. In Patent Document 1, it is mentioned that a splice point exists at every 1 km or so, thereby causing splice loss in an optical fiber transmission line. Also, it is indicated that the repeater interval is usually 40 km or 80 km and that the repeater interval of 80 km or more is preferable where possible, because the link cost for an interval of 40 km would be two times as much as the link cost for an interval of 80 km.
International Publication No. 2009-107260 (Patent Document 2) discloses an invention of a terrestrial optical fiber transmission line. In Patent Document 2, it is indicated that in the case of optical fiber cables installed at present as a terrestrial transmission line in Japan, the span between optical transmission devices is 80 km and a splice point exists at every 2 km on the average. It is also stated that in the case of optical fibers having a large mode field diameter, even if an axial misalignment occurs when the fibers of the same kind are fusion spliced, the splice loss due to splicing is small, since the axial misalignment has relatively small influence on the splice loss because the ratio of the axial misalignment relative to the size of the mode field diameter is small.
Y. Yamamoto, et al, OECC2011, pp.241-244 (2011) (Non-patent Literature 1) indicates that an optical transmission fiber is connected to a pigtail of apparatus, such as an optical fiber amplifier provided in a repeater of an optical fiber communications system. In many cases, the pigtail of apparatus is a standard single mode optical fiber (SSMF) based on International standard ITU-T G. 652.